From white dwarfs to flashing supernovas

Scientists tackle a chicken-or-egg question: Is the collision that creates a supernova caused when a white dwarf takes on too much material from other stars or when it crashes into another white dwarf?

Supernovas in space are caused when a white dwarf explodes, and they are key events in cosmology. Scientists use these important events, called Type 1a supernovas, as “candles,” or markers to measure distances in the cosmos. However, they have never determined if a white dwarf explodes because it is taking on too much material from other stars, or because it is crashing into another white dwarf. The New York Times reports that scientists may have found an answer.

In a paper published in the journal Nature, Marat Gilfanov and Akos Bogdan of the Max Planck Institute for Astrophysics in Germany report that some supernovas, at least those produced by stars known as ellipticals, are mostly produced by collisions between white dwarfs. Gilfanov told the NY Times, “We have revealed the source of the most important explosions in cosmology.” The scientist further adds that, until recently, they did not know exactly what kind of sources these were.

Supernovas are believed to contribute to the “dark energy” that is thought to be speeding up the expansion of the universe. Scientists say this discovery shows that “no more than 5 percent” of the supernovas in older stellar systems could be produced by swelling white dwarfs that were gobbling up gas from their neighbors. But this new discovery confirms that there may be two different types of Type 1a supernovas in the cosmos: ones caused by colliding dwarfs, and ones caused by swelling dwarfs.

Further, this discovery means that using Type 1a supernovas as the standard to measure distances in the galaxy could be problematic. Swelling or accreting white dwarfs explode at a precisely determined mass scientists call the Chandrasekhar limit. But if two dwarves are colliding, they would have all sort of different mass sizes.

Hopes are that this question will soon be clarified. Adam Riess is a “dark energy hunter” from Johns Hopkins University and the Space Telescope Science Institute. As he wrote to the NY Times, “If we find a connection to where nature does it one way versus the other, we could use that information to improve the use of these candles. I think we are getting close to that point now.”